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由于截图时可能需要精确截取某一部分，所以需要放大镜的功能，这样截取的时候才更容易定位截图的位置。

添加PictureBox，name属性设置为“pictureBox_zoom”；

在“Form1_Load”事件处理函数中添加以下代码：

//设置放大镜的大小
            this.pictureBox_zoom.Width = this.ZoomBoxWidth;
            this.pictureBox_zoom.Height = this.ZoomBoxHeight;

在“ExitCutImage”方法中添加代码：

在“Form1_MouseUp”事件处理函数中添加代码：

在“ShowForm”方法的else条件最后添加代码：

if (this.ZoomBoxVisible)
                {
                    UpdateCutInfoLabel(UpdateUIMode.ShowZoomBox);
                    this.pictureBox_zoom.Show();
                }

在“UpdateCutInfoLabel”函数最后添加以下代码：

if (this.pictureBox_zoom.Visible || (updateUIMode & UpdateUIMode.ShowZoomBox) != UpdateUIMode.None)
            {
                Point zoomLocation = new Point(MousePosition.X + 15, MousePosition.Y + 22);
                if (zoomLocation.Y + this.pictureBox_zoom.Height > this.Height)
                {
                    if (zoomLocation.X + this.pictureBox_zoom.Width > this.Width)
                    {
                        zoomLocation = new Point(MousePosition.X - this.pictureBox_zoom.Width - 10, MousePosition.Y - this.pictureBox_zoom.Height - 10);
                    }
                    else
                    {
                        zoomLocation = new Point(MousePosition.X + 15, MousePosition.Y - this.pictureBox_zoom.Height - 15);
                    }
                }
                else
                {
                    if (zoomLocation.X + this.pictureBox_zoom.Width > this.Width)
                    {
                        zoomLocation = new Point(MousePosition.X - this.pictureBox_zoom.Width - 15, MousePosition.Y);
                    }
                }
                this.pictureBox_zoom.Location = zoomLocation;
                if (!this.pictureBox_zoom.Visible)
                {
                    this.pictureBox_zoom.Show();
                }
            }

在“Form1_KeyUp”事件处理函数中添加以下代码：

为“pictureBox_zoom”添加“Paint”事件处理程序，代码如下：

        /// <summary>
        /// 放大镜组件重绘事件处理程序
        /// 实时显示鼠标指针位置放大后的图像
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void pictureBox_zoom_Paint(object sender, PaintEventArgs e)
        {
            Bitmap bmp_lbl = new Bitmap(e.ClipRectangle.Width, e.ClipRectangle.Height);
            int srcWidth = (int)(this.ZoomBoxWidth / 10);
            int srcHeight = (int)(this.ZoomBoxHeight / 10);

            Bitmap bmp = new Bitmap(srcWidth, srcHeight);
            Rectangle srcRect = new Rectangle(MousePosition.X - 5, MousePosition.Y - 4, srcWidth, srcHeight);
            if (!isCuting)
            {
                srcRect = new Rectangle(MousePosition.X - 6, MousePosition.Y - 5, srcWidth, srcHeight);
            }
            Graphics g = Graphics.FromImage(bmp);
            g.DrawImage(screenImage, 0, 0, srcRect, GraphicsUnit.Pixel);
            g.Dispose();

            //Zoom
            int x, y;
            for (int row = 0; row < bmp.Height; row++)
            {
                for (int col = 0; col < bmp.Width; col++)
                {
                    Color pc = bmp.GetPixel(col, row);
                    for (int h = 0; h < 10; h++)
                    {
                        for (int w = 0; w < 10; w++)
                        {
                            x = col * 10 + w;
                            y = row * 10 + h;
                            if (x < bmp_lbl.Width && y < bmp_lbl.Height)
                            {
                                bmp_lbl.SetPixel(x, y, pc);
                            }
                        }
                    }
                }
            }

            e.Graphics.DrawImage(bmp_lbl, 0, 0);

            int blockX = e.ClipRectangle.Width / 2;
            int blockY = e.ClipRectangle.Height / 2;

            SolidBrush brush = new SolidBrush(Color.FromArgb(10, 124, 202));
            Pen pen = new Pen(brush, 2.0F);
            e.Graphics.DrawLine(pen, new Point(0, blockY), new Point(e.ClipRectangle.Width, blockY));
            e.Graphics.DrawLine(pen, new Point(blockX, 0), new Point(blockX, e.ClipRectangle.Height));

            g.Dispose();
            bmp_lbl.Dispose();
        }

编译，运行，截图看看效果吧！

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